The present invention is directed to an ion source using a cathodic vacuum arc, particularly to an ion source using a filtered cathodic-arc for the production of dense, adherent coatings, for example, wherein the filtering eliminates or reduces macro-particles normally produced by the cathodic arc, and more particular to a magnetic-cusp for a cathodic-arc which allow high magnetic fields required for good ion transport, while providing a low impedance path for electrons from cathode to anode, giving stable arc discharges.
Cathodic arcs produce a highly ionized metal vapor which has proven useful in the production of dense, adherent coatings. For many applications, macro-particles normally produced by the cathodic arc are unacceptable and must be filtered out. Thus, the separation or elimination of macro-particles from the ion flux produced by a cathodic arc discharge has long been the goal of many research efforts.
A number of approaches have been advanced for the removal of such macro-particles, which include the use of filtering. Recently, two micro-particle filtered cathodic arc sources have been developed which address the basic issues of arc control, transport of metal ions through the filter, and shielding the source from line-of sight of the parts to be coated. Both of these micro-particles filtered cathodic arc sources rely on electrostatic fields produced by the flow of magnetically constrained electrons through the filter to guide the ions from the cathode to a substrate to be coated. These filtered cathodic arc sources are disclosed and claimed in U.S. Pat. No. 5,279,723 issued Jan. 18, 1994 to S. Falabella et al., and U.S. Pat. No. 5,282,944 issued Feb. 1, 1994 to D. M. Sanders et al.
While these above-identified filtered cathodic arc sources provide the capability of producing coatings without blemishes caused by macro-particles, the present invention provides an improved cathodic-arc arrangement for the filtered cathodic arc source of above-referenced U.S. Pat. No. 5,279,723 utilizing a magnetic cusp which provides a straight-through magnetic field which matches well to the "knee-type" or bent macro-particle filter arrangement for this patent. The magnetic cusp of this invention allows high magnetic fields required for good ion transport, yet provides a low impedance path for electrons from cathode to anode, giving stable arc discharges.